The present invention is related to a new process for telomerizing conjugated dienes and a new composition useable in the telomerization of conjugated dienes.
The catalytic dimerization of dienes under the concomitant addition of a nucleophilic reagent was reported simultaneously in 1967 by Smutny at Shell and Takahashi at Osaka University. The reaction is defined under the general term of telomerization as the dimerisation of conjugated diolefins (taxogens) together with the addition of a third molecule (telogen) over one double bond equivalent. Telogens can be for example alcohol, amine (I and II), methylene group, silane, carboxylic acid, water, etc. (see scheme 1) leading to heavier organics (ethers, amines, silanes, esters, alcohols, etc.). 
For example U.S. Pat. No. 4,142,060 is related to a process of telomerizing dienes with a telomerizing compound (e.g. methanol, water, etc.), comprising the reaction of a diene with a telomerizing compound with at least one mobile hydrogen atom in the presence of a water-soluble catalytic system comprising at least one certain water-soluble phosphine and a transition metal, preferably palladium or a palladium containing compound.
WO 98/08794 discloses a process for telomerizing dienes with a telogen containing a reactive hydrogen atom in the presence of a palladium compound and a specific water-soluble phosphine.
Using water as a telogen the reaction with butadiene is usually designated as hydrodimerization. The telomerization of butadiene with water is described for example in U.S. Pat. Nos. 5,043,487, 5,345,007, 4,356,333, EP-A-0,436,226, WO 95/30636 and U.S. Pat. No. 4,417,079.
The telomerization of butadiene with methanol (MeOH) has been extensively investigated. While some activity was observed for a variety of metals, cobalt, rhodium, nickel, and platinum, palladium based systems are superior both in terms of activity and selectivity. Conventional systems commonly associate a mixture of palladium(II) and phosphine ligands and lead mainly to the formation of trans and cis-1-methoxy-2,7-octadiene (t-I and c-I) and 3-methoxy-1,7-octadiene (II) and the octatriene III as a by-product (see for example U.S. Pat. No. 4,142,060). 
Telomerization of 1,3-butadiene with an alcohol has recently gained increasing interest for the synthesis of linear ethers. These products, after hydrogenation of the remaining olefinic double bonds, can be particularly useful as fuel additives or plasticizers. 
Works described in the last twenty years concentrate on the study of the reaction under homogeneous conditions. The separation of the homogeneous catalysts, typically palladium based, from the products is a significant factor in the economics of the application of this powerful reaction. It is now generally accepted that the use of two-phase catalytic systems is an approach that could overcome of the separation problems by allowing the phase separation of the products from the catalyst phase.
Recently, non-aqueous ionic liquids have been attracting attention for the application of many homogeneous reactions to biphasic systems (see for example the reviews xe2x80x9cIonic Liquidsxe2x80x9d of J. D. Holbrey, K. R. Seddon in Clean Products and Processes 1 (1999) 223-236 and Welton, T. Chem. Rev. 1999, 99, 2071-2083).
EP-A-0,776,880 (corresponding to U.S. Pat. No. 5,874,638) discloses for example a process for the hydroformylation of olefinic compounds in the presence of an ionic liquid.
J. Dupont et al. (Organometallics 1998, 17, 815-819) disclose a catalytic process of hydrodimerization of 1,3-butadiene by palladium compounds dissolved in ionic liquids. As palladium catalyst compounds [(xcex73-C4H7)Pd-xcexc-Cl]2, [(xcex73-C4H7)Pd(1,5-cyclooctadiene)][BF4] and palladium acetate have been used which are told to be completely soluble and stable in the ionic liquids 1-n-butyl-methylimidazolium tetrafluoroborate (BMI+.BF4xe2x88x92) and 1-n-butyl-methylimidazolium hexafluorophosphate (BMI+.PF6xe2x88x92) at room temperature. At the end of the performed hydrodimerization reactions however metallic palladium was detected thus limiting the reutilization of the catalytic system. This has been attributed to the instability of these catalysts to water. The formation of metallic palladium could be suppressed by the use of a new catalyst precursor (BMI)2PdCl4 which has been obtained by reacting PdCl2 with a 2 molar excess of 1-n-butyl-3-methylimidazolium chloride in acetonitrile at reflux temperature. However even for this stable catalyst conversions reported were low.
In an attempt to use conventional palladium phosphine catalysts in the presence of ionic liquids such as the above mentioned 1-n-butyl-methylimidazolium tetrafluoroborate (BMI+.BF4xe2x88x92) or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI+.TF2Nxe2x88x92) for the telomerization of butadiene for example with methanol, the present inventors found surprisingly that the conventional palladium phosphine catalyst system in the presence of ionic 1,3-dialkylimidazolium liquids in contrast to the above mentioned catalyst compounds like [(xcex73-C4H7)Pd-xcexc-Cl]2, [(xcex73-C4H7)Pd(1,5-cyclooctadiene)][BF4] or palladium acetate shows almost no reactivity, and thus was not available for a telomerization process in the presence of the ionic liquid.
The object underlying the present invention was to find a new catalytic process for telomerizing a conjugated diene wherein a highly active and selective catalyst system can be used which allows the formation of the diene telomers with high yields and selectivity and which also allows a simple separation and recycling of the catalyst system.
In accordance with the present invention there is provided a new process for telomerizing a conjugated diene which comprises reacting said conjugated diene with a compound containing active hydrogen in the presence of a catalyst system comprising at least one transition metal compound, at least one phosphorus-containing compound, and at least one salt which forms a liquid under the conditions of the telomerization process.